Wet strength tester



July 7, 1959 H. T. FISHER Erm. 2,893,241

vWET* STRENGTH TESTER Filed sept. 5o, 1955 BSheQtS-sheet 1 `luly 7, 1959H. T. FISHER ET AL WET STRENGTH TESTER 5 sheetssheet 2 Filed Sept. 30,1955 HEM/ey THOMAS F/.sf/f/e F IG IA JAW/E5 Mae/w NToR PATENT AGENT July7, 1959 H. T. FISHERI ET AL. 2,893,241

WET STRENGTH TESTER Filedept. so, y1955 5 sheets-sheet s Tra/@Mey July7, 1959 H. T. FISHERv ET Al.

WET STRENGTH TESTER 5 Sheets-Sheet 4 Filed Sept. 30, 1955 @n 2 .1M L

United States Patent O WET STRENGTH TESTER Henry Thomas Fisher, St.Catharines, Ontario, and James Moran, Baie Comeau, Quebec, Canada,assgnors to The Ontario Paper Company Limited, Thorold, ntario, CanadaApplication September 30, 1955, Serial No. 537,864

' 4 clams. (c1. 13-159) 'This invention relates to the paper making art,and more particularly to a means and method of determining the strengthof a wet paper web.

In the course of manufacture of paper from pulp it is often desirable toestimate in advance the probable tensile strength of the paper web atvarious stages of its manufacture on the paper machine and thus of thestrength of such web at varying moisture contents. In particular thestrength of such sheet at the end of the Fourdrinier wire when the saidsheet is of the order of 18% dry and also throughout the press sectionwhere additional water is removed up to about 33% dry is critical tosatisfactory machine operation. The adequacy of strength of pulp inpaper furnish is determined by preparing a test sheet of paper from suchpulp by well known methods, eg. Oiiicial Standard Method No. T-205- m53of the Technical Association of the Pulp and Paper lndustry, but testson such test sheets correlate to the properties of iinished paper, e.g.in the case of newsprint to a sheet about 92% dry and do not providepertinent data as to the papermaking characteristics of such pulp in thewet state as above described. The present invention provides a means ofpreparing and testing similar test sheets of pulp in a manner which doesprovide, the required information as to the character of the paper webat the wet end of the paper machine. Such testing becomes of particularimportance in high speed papermaking machines where breaks in the paperweb can cause costly delays.

In the past, methods devisedfor the testing of the wet paper web havebeen unsatisfactory. It will be appreciated that the wet sheet isextremely weak and easily damaged in handling, for example the handlingrequired to transfer the wet sheet to a tensile tester, and clamping insuch tester. Such a method has frequently damaged or weakened the sheetto a degree that the results of the testing have been substantiallymeaningless.

It is an object of this invention, therefore, to provide a means andmethod of testing the wet strength of a paper web which will give moreaccurate and significant results than has heretofore been possible.

It is another object of this invention to provide a wet web strengthtester in which the possibility of damage to the web prior to making thedesired strength measurement is practically eliminated.

These and other advantageous objects will become apparent through aconsideration of the following detailed description taken in conjunctionwith the attached drawings in which Figure l is a vertical cross-sectionthrough the paper forming portion of a tester constructed so as toembody features of this invention. i

Figure 1A is a drawing similar to Figure 1 showing the suction apparatusattached to the drain and also showing the components more specicallyillustrated in Figures 1- 70 and 6.

'2,893,241v Fatented July 7, 1959 Figure 2 is an elevational view of theapparatus shown in Figure l.

Figure 3 is a front elevation, partly in section of tensile testerconstructed so as to embody features of this invention.

Figure 4 is an exploded perspective view of the grid and supporting wireforming part of the apparatus illustrated in Figure 1.

Figure 5 is a perspective view of the split forming wire, and

Figure 6 is a detailed view similar to Figure 1 of a portion of theapparatus shown in Figure 1.

This invention consists broadly in a method of forming a wet paper testsheet upon a forming wire which is split on a centre line andsubsequently placing the forming wire with the test sheet intact thereonin a device by which the two portions are displaced from each other soas to cause rupture of the sheet, the force required to effect suchdisplacement and rupture giving a measure of the zero-span tensilestrength of the wet paper test sheet formed thereon. This invention alsoprovides means whereby the moisture content at the time of testing ofsuch wet paper test sheet may be substantially predetermined.

The drawings illustrate a specific apparatus for forming a wet testsheet upon the split wire, and an auxiliary apparatus for applying theforce to separate the portions of the wire and thus break the testsheet, both of these being designed to effect the purpose of thisinvention.

Referring firstly to the sheet forming portion of the apparatusillustrated in Figures 1 and 2, a reservoir 1, here shown as cylindricalin form, having suitably arranged mounting means at its lower end(indicated generally as at la), is secured as by hinges 2 to base member8. An O-ring seal 3 located in a suitable channel provides a water-tightseal when the apparatus is in closed position as shown in Figure l. Twoclamps 4 are adapted to retain the cylinder tightly in closed positionagainst the O-ring seal 3, the clamps being rotatably affixed to thecylinder mounting la and cooperating with a projection 8a in the basemember 8 when in closed position. The mounting 1a of cylinder 1 bears nclosed position against carrying ring 6 of the forming wire cloth 5through the O-ring 3, the carrying ring 6 being adapted to be insertedin a seat formed in the base member 8 and on a fixed ring 7 in which ismounted a supporting grid 7a and a supporting wire 7b. (See Figure 4.) Afurther O- ring seal 11 mounted in a suitable channel completes thewater tight seal between the carrying ring 6 and the base member 8.

Thus, as is shown, the removable carrying ring 6 is mounted upon thebase member 8 with O-ring seal 11 completing the seal. The carrying ringalso ts on top of the supporting wire 7b and grid 7a, this grid 7aconsisting of parallel stainless steel strips fitting loosely into slotsin the supporting ring 10 and supporting a coarse wire 7b which isfastened to the supporting ring by a bezel ring 16. The forming wirecloth 5 thus rests upon and is supported by the grid 7a and the coarsewire 7b mounted upon the grid.

The lower portion of base member 8 is inwardly tapered as shown andterminates in a drain pipe 13. The drain pipe may conveniently beattached to a source of vacuum as applied from the vacuum pump 13f, theline 13e, the reservoir 13d, the line 13C and the valve 13b. The watersupply may also be conveniently connected to said drain pipe controlledthrough the Valve 13g to.

the pipe 13h. The forming wire consists of a diametrically split wire ofproper mesh to form a paper sheet. Although the split wire 5 rests uponthe supporting wire, the split wire must itself possess rigidity andstrength to fied long crimp twill weave wire 64 x 48 mesh has beenemployed by `us and is satisfactory for this purpose. The wire issoldered or otherwise securely affixed to the underside of the wire ring5a which is similarly split.. The wire ring portions 5a are located by akeyway (not shown) into the carrying ring 6 with the two portions of thewire ring contiguous and so that the inside of the wire forms acontinuous plane surface transversely across the cylinder bore.

' It will be appreciated that the splitting of the forming. wire clothand the mounting thereof on corresponding sections of the wire ring mustbe carried out carefully and accurately to achieve continuity in wirepattern over the meeting line. Generally, it is believed that bestresults will be achieved if the wire is cut into half prior to mountingin the wire ring. During the operation of joining the split wire to thecorresponding wire ring section, a continuous stress should bemaintained parallel to the split and close to the meeting line. Thecompleted wires will then be stressed throughout and when the wire ringsare placed together in the carrying ring, the wire will form a taut,uninterrupted surface. If this splitting and mounting operation iscarried out with care and precision, the wires in the two halves willmeet continuously across the gap, and the split will be virtuallyundetectable in the formed sheet. Tests on paper formed on this splitwire and subsequently dried have shown no significant difference instrength properties between the region over the meeting line and theremainder of the sheet.

To reduce the water content of the formed sheet to the desirablemoisture content, vacuum is applied. It has been found preferable (butnot essential) to carry out this part of the procedure on a separatepart of the apparatus. In Figure 6 base member 51 is identical with basemember 8 of the sheet forming apparatus. It is fitted with a ring 52identical in diameter with ring 10 on the sheet forming apparatus butresting on springs 53. A supporting wire and grid 54 (identical with 7)with its -bezel ring 55 (identical with 16) is fitted in base member 51.If it is desired to accomplish this part of the operation in theequipment of Figure 1 only, then the spring lifting mechanism shown as52-53 of Figure 6 can replace element 10 of Figure l.

The procedure in forming the test sheet is as follows:

The wire rings 5a are fitted into their appropriate keyways in carryingring 6, the split wire then presenting a plane continuous surface. Thecylinder reservoir 1 is swung back on hinges 2 and the carrying ringplaced in its seat and with the wire portion thus supported by andresting on the supporting wire 7b and grid 7a. The cylinder is thenswung down and locked in place by clamps 4, the whole assembly byO-rings 3 and 11 forming a water tight seal. Suicient water is added tothe cylinder to cover the wire. Such water may be added through a `valveconnection in the drain pipe, the water supplied rising up through thegrid and forming wire. A measured quantity of pulp stock is then addedin the form of a dilute suspension and the water level raised to apredetermined standard level through the further addition of water. Thediluted stock in the cylinder should then be stirred and the cylinderthen drained through drain pipe 13 by opening aquick-opening drain valve(not shown). The cylinder reservoir 1 is then swung back on its hinges2. The carrying ring 6 holding the forming wire with the formed sheet istransferred on to the vacuum drying arrangement as shown in Figure 6.Prior to inserting the carryingY ring a wetted blotter 30B is laid on tothe supporting'wire and grid 54. The use of this blotter is toobtainuniform moisture distribution in the formed testv sheet. The carryingring isV then pressed down and' vacuum applied for such a length oftimey aste` give approximately a predetermined moistureAV cnntentirr thetest: sheet; the 'required times have' been determined on the basis ofprevious experience with the equipment. When the vacuum is released thespring loaded ring 52 automatically lifts the forming wire from thesupporting wire thus preventing reabsorption of moisture from theblotter. The test sheet is now ready for testing and is carried on theforming wire in the carrying ring to the tester'.

The tensile tester may be any apparatus designed to displace the twoportions of the split wire with the test sheet intact thereon from eachother and thus cause rupture of the sheet, and to record the forcerequired to effect such rupture. y

Such a device may take the form shown in Figure 3.

This drawing shows` ai chain loaded balance type of tensile tester. Inoperation, the carrying ring with the forming wire and formed sheet areplaced on a raised hydraulic jack. The jack now lowers automaticallyleaving the two halves of the forming wire on the movable -head 21 andthe fixed head 22. The movable head is then pulled via a linkage system30, 31, 32 and 33 by a chain balance. When the sheet breaks the balanceloading is stopped' and the breaking load is noted on scale 34. The twoheads 21 and 22 are provided with machined top surfaces onto which thewire ring is seated, and locating means such as pins 21a and 22a whichserve to locate and hold the wire.

. The chain balance is driven by a constant speed motor 24 with speedreduction effected both in the motor ygear box. and in a further gearbox27 at the top ofthe shaft.

The electric motor runs continuously during operation of the tester. Thetest is eected by engaging the motor clutch 26 and starting the loading'of the balance. When the sheet breaks or the indicator reaches the endof the scale 34' the clutch disengages.

After thesheet breaks the breaking forc'e is read from the' indicator 37on scale 34. The two halves of the sheet are then' removed and weighedto determine the total weight and then dried and weighed to determinethe percentage dry' solids.

We have' described: the above specic apparatus designed to carry outVour invention. It will be obvious that considerable variation is`permissible in the dimensions and minor detailsV of the apparatus and itis to be strictly understood that our invention isv not to be deemedlimited to' such specific apparatus or to the construction of detailsthereof. Such embodiments of the invention as come within the scope andpurview of the appended claims are to be considered as partof thisinvention. As an example of certain dimensions and apparatus detailswhich we have found satisfactory, the following may be noted.

The cylinder 1V maybe 4" in diameter.

The coarse wire 7b supporting the wire on which thev wet sheet is formedmay be ZOmesh.

A groove maybe engraved on'the inside of the cylinder I at a distancevofv 13'^%1"`abovel the surface of the wire to indicate the maximum levelduring filling of the cylinder with water prior toV drainage in sheetformation.

The effective hydraulic legpr'oviding drainage may be 31.5, this beingthe distance from the forming wire to the out-flow levelof a water seal.

The vacuum applied t'o the web for adjustment of moisture content may be20 of mercury. With the apparatusv which wey have constructed theapplication of such vacuum permits'adjustment ofthe solids content of apulp sheetof newsprint furnish substantially as follows:

Time of vacuum: Solids content, percent of 0.416r0-004 gram equivalentdry weight. Such a weight lof sheet corresponds closely to a basisweight of 32 1b. per 3,000 sq. ft. and is a suitable weight of sheet forinvestigation of the wet strength of newsprint furnishes. A trial sheetis normally made and its weight used to calculate the exact volumerequired to give a sheet weight as above for any given stock.

The pertinent information to be derived from our invention is a measureof the substantial zero-span tensile strength of a wet pulp sheetcorrelated to the moisture content of such sheet. It is convenient torecord the tensile strength in terms lof grams per millimetre of web atthe break, and the scale of the tensile strength tester chain balance aspreviously described may be calibrated directly in such units. We havefound that in general for a given pulp the relation of the abovezero-span Weight tensile strength expressed in grams per centimetre ofweb at the break is linear with respect to moisture content over the7%-22% solids range. A graph may therefore be plotted from a series oftests on individual sheets of a given pulp and we have found the abovetensile strength at 20% equivalent dry solids obtained from such a graphtogether with an indication of the slope of the tensilestrength-moisture relationship on such graph to be an overall andcomprehensive measure of the strength of a wet sheet of a given pulpwhich measure is the specic object of this invention.

The above information, relative to details of apparatus land procedureof using it, has reference to a preferred method of applying ourinvention to determine the wet strength of pulp and is given by way ofexample only and it is obvious that anyone skilled in the art mayintroduce modifications therein without departing from the spirit andintent of our invention.

What we claim as our invention is:

l. Apparatus for forming a paper test sheet comprising a reservoir forpaper stock, said reservoir having an outlet, a removeable forming wirecloth located at the outlet of said reservoir, said forming wire clothbeing formed in two separable sections located so as to form asubstantially continuous paper forming surface, a source of vacuumbeneath said forming wire cloth, and means for preventing thereabsorpton of water withdrawn through said source of vacuum by theformed paper test sheet.

2. Apparatus as claimed in claim l wherein said means comprises a springloaded retaining means for both sections of said forming wire cloth,said spring load being such as to be overcome by the force exerted onthe test sheet by said vacuum, but such as, when such vacuum isreleased, to raise both sections of said forming wire cloth free of saidvacuum source.

3. The method of determining the substantially zero span wet tensilestrength of a paper sheet which consists in forming a test sheet yofsubstantially predetermined solids content on two separable sections offorming wire cloth, the wire cloth sections being positioned adjacenteach other to provide a continuous forming surface, applying a force tothe test sheet to cause its failure in tension substantially at themeeting line of the wire cloth sections while it is still positioned onthe said sections and indicating the force required to effect suchfailure in tension.

4. The method of determining the substantially zero span wet tensilestrength of a paper sheet which consists in forming a test sheet ofsubstantially predetermined solids content on two separable sections offorming wire cloth, the wire cloth sections being positioned adjacenteach other to provide a continuous forming surface, applying a force tothe test sheet to cause its failure in tension substantially at themeeting line of the wire cloth sections while it is still positioned onthe said sections, indicating the force required to effect such failurein tension and measuring the moisture content of said sheet.

References Cited in the ile of this patent UNITED STATES PATENTS1,193,613 Riegler Aug. 8, 1916 1,514,236 Smith Nov. 4, 1924 2,469,013Sobota May 3, 1949 FOREIGN PATENTS 24,891 Finland Sept. 26, 1951

